1. Field of the Invention
This invention relates to a multiplex transmission system of the type used in automotive applications for transmitting serial data message formats among a plurality of multiplex nodes connected to a common multiplex transmission line, and more particularly to a pulse width modulation multiplex transmission system operated in accordance with Society of Automotive Engineers standard J1850.
2. Prior Art
Messages transmitted from an originating node in a multiplex communication system normally include priority/type bytes describing the group or function of the nodes that should receive the message, in addition to target bytes that may define the specific address or addresses nodes to receive the message. The transmitting node must receive confirmation or acknowledgment that the addressed node has received the message.
A typical received node includes interface circuitry that includes programmable memory for storing the address of the node as well as the priority and/or type functions for which the node is responsible. These stored type and target bytes must then be compared by the interface circuitry with the type and target bytes of all incoming messages in order to determine if the message should be received and processed. Since programmable memory within the interface circuit represents an added cost that increases complexity without increasing functionality, it is desirable to provide a node interface circuit that offloads this function to the host microprocessor at the node that already includes programmable memory and comparators capable of performing this function.